In my experience, if your ferts are preferential towards a kibble, particularly a cat food, which has a lot of "flavor" ingredients added to make it palatable, (since it is so nutritionally incomplete domestic pets wont eat it without enticement), your critters will most likely reject any radical changes to their staple, such as a first time offering of duck soup.
I would immediately change to a premium ferret kibble, and if it were me, although a gradual swap is usually recommended, i would go cold turkey. You may have to buy an expensive bag of really high quality food with good taste to get them to accept the change happily the first time, after that you can slowly transition them to any permanent brand you choose.
After a week on the new kibble, i would begin to wet the dry down with some ferret-tone and swirl it around in the bowl so that the amount coats the food evenly and doesnt modify the flavor too much...
Once they get used to that change, you may want to profer them some raw items... as supplimental. My regular treats are heavy whipping cream, (high fat), mixed with a small amount of pro-biotic acidophilus milk, scrambled eggs, pureed raw catfish, pureed chicken liver.
They are very particular, i can usually only get 1 or 2 of the 4 to eat any given treat, the rest reject it, but between them, they all get somthing... all except my male.. who honest to god needs it the most as he has endocrine disease >.< All he wants is his kibble, but at least he gets the ferret-tone with it.
<message edited by Buffmuffin on Monday, February 16, 2009 5:07 PM>